So-called third generation (3G) mobile communication networks are currently being deployed. In Europe such networks conform to various standards formalized by the 3rd Generation Partnership Project (3GPP), which has a number of versions, generally known as releases.
The high price paid for the licenses to operate 3G networks, in particular in Europe, together with the potential high cost of 3G network infrastructure deployment, has motivated network operators to develop innovative strategies in network infrastructure deployment.
One effective way to reduce the investment costs and risks of a fast 3G network deployment is for operators to share parts of, or the whole of, their 3G network infrastructure. In the current dynamic market place, as a result of partnerships, acquisitions, creative agreements and such like amongst operators, equipment manufacturers and service providers, the need for tools that enable various degrees of network sharing is becoming more and more important.
Typically sharing partners have their own dedicated networks, and a further shared network is provided in which all the sharing partners provide services. In 3GPP release 5 (REL-5), a concept known as UTRAN (UMTS terrestrial radio access network) sharing has been introduced in order to bring mobility and access control features to allow correct operation of shared networks. In “UTRAN sharing” the radio access network is divided into shared network areas, which shared network areas further consist of one or more location areas. A user equipment is allowed access to a network area only if it is authorized to. Thus networks must be provided with means for determining whether network access by a particular user equipment is allowed, and preventing a call being established if it is not. Thus a call may not be established if the user equipment is not authorized for the network, or a call may be dropped if a user equipment moves to an unauthorized network.
A basic principle in mobile communication networks, however, is that an emergency call should never be dropped or caused to be dropped due to roaming or other access control restrictions applicable for normal roaming, calls, packet-switched sessions, or other types of transactions.
The proposals for UTRAN sharing in 3GPP REL-5, however, provide for authorization checks to be performed in shared networks such that a call may be terminated if a user equipment (UE) is currently in, or moves into, a network area for which calls are not authorized. This presents the possibility of the shared network control features terminating an emergency call.
In proposals for shared networks, it has been proposed that as part of the establishment of the call, a core network returns to a radio access network the shared network area (SNA) access information (AI) for the UE associated with the call establishment. The radio access network may then use this information to reject the call initially, or ‘drop’ the call if the UE moves to a network for which call connections are not authorized.
More specifically, in current proposals the core network provides SNA AI to the UTRAN after the signaling connection establishment. SNA AI consists of a set of PLMN (public land mobile network) identities (PLMN-ID), and a set of shared network area codes (SNAC) for each PLMN, which codes indicate the areas the UE is allowed to access. The UTRAN performs access control based on the received user specific SNA AI. That is, the UTRAN allows the UE to access only those shared network areas identified in the SNA AI. If there are no allowed shared network areas available, or if the UE is currently in a ‘forbidden’ network, then the UTRAN initiates connection release towards the core network and the call is released according to 3GPP REL-5 specifications.
However, as discussed above in the event of an emergency call, the call should not released even if there are no allowed shared network areas available.
In accordance with current 3GPP REL-5 specifications, there is a proposal for handling (circuit switched) emergency voice calls if the RNC and the circuit-switched domain of the core network know that the call is an emergency call. In such circumstances, the circuit switched core network sends a RANAP:COMMON ID message as soon as the IMSI is known, but does not send the SNA AI for the UE. By not transmitting the SNA AI, it is intended that this access information cannot be used to terminate the emergency call, and hence the emergency call will not be dropped due to the SNA access restraints for the UE.
However a problem may arise with this proposal, where a new call between the UE and the network is established in the packet switched domain of the core network, whilst the emergency call in the circuit switched domain is ongoing. The establishment of the packet-switched call may result in the SNA AI being provided to the radio network controller (RNC) of the UTRAN. Thus the RNC may obtain the SNA AI and use this information, potentially leading to the emergency call being dropped.
A further problem may arise if relocation occurs, and the call is transferred to a different network. In such a case, a handover to a target network is performed for the circuit switched emergency call, and its connection (Iu-cs) is relocated to a given target RNC. As a result of this relocation, and as proposed by 3GPP REL-5, the packet switched core network may send the SNA AI for the UE to the target RNC. Thus the target RNC is provided with SNA AI which may cause the emergency call to be dropped.
It is an aim of the invention to address one or more of the above-stated problems.